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Research conducted at UB suggests that high-altitude cerebral edema is caused by a disruption in the blood-brain barrier, the specialized layer of cells in cerebral blood vessels that, under normal conditions, allow only certain substances to pass into the brain's circulation.
John A. Krasney, professor of physiology and a specialist in hypoxia, presented the findings April 28 at the 66th annual meeting of the American Association of Neurological Surgeons in Philadelphia.
"Brain swelling, and also pulmonary edema [fluid in the lungs], is one of the major problems at high altitude and we don't really know the cause of either," Krasney said. "It is not lack of oxygen per se. At high altitude, the brain has an adequate supply of oxygen because blood flow increases to compensate for the lower concentration of oxygen in the air. Yet people still get sick."
In its mildest form, swelling of the brain brings on the headaches and nausea characteristic of acute mountain sickness. In its most severe form, unrelieved by retreat to lower elevations, brain swelling advances to high-altitude cerebral edema, which causes disorientation, impaired mental function and death.
Krasney's research using sheep has shown that the symptoms of high-altitude cerebral edema are not caused by an inadequate supply of oxygen or glucose to the brain. Rather, it appears that an accumulation of malfunctions creates enough cerebral blood pressure to force apart cells of the blood-brain barrier and allow fluids to accumulate in and around brain tissues.
The researchers theorize that acute hypoxia may allow a decline in cyclic adenosine monophosphate (cAMP), a chemical messenger involved in regulating capillary permeability. The decrease in cAMP may allow the cerebral capillaries to leak.
In addition, Krasney said, it is possible that, in the presence of hypoxia, another chemical messenger, cyclic guanosine monophosphate (cGMP), acts with nitric oxide, a vasodilator, to promote and sustain permeability of the blood-brain barrier. The combined influence of actions could allow fluid to accumulate in the intracellular spaces, he said.
Yet another mechanism that may be at work involves elevated levels of leukocytes that may cling to the lining of cerebral blood vessels and cause leaks in the blood-brain barrier.
Krasney and colleagues are attempting to clarify further the importance of these mechanisms in the development of acute mountain sickness and high-altitude cerebral edema.
Their research is supported by the National Heart, Lung and Blood Institute.
source:www.buffalo.edu/reporter
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